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| Fig. 1: A visual of the effects of topsoil erosion in a wheat field near Washington State University. (Source: Wikimedia Commons) |
With the world population projected to grow to 9.6 billion people by 2050, feeding the people on our planet will undoubtedly be a considerable challenge. [1] Unfortunately, topsoil erosion is threatening to make this daunting task considerably more difficult than it already is. Soil erosion is a huge problem, yet it is hardly ever talked about by the media or public. Cornell ecology professor David Pimenel explains, "Soil erosion is second only to population growth as the biggest environmental problem the world faces. Yet, the problem, which is growing ever more critical, is being ignored because who gets excited about dirt?" [2] In fact, some experts fear that the world will run out of usable topsoil to grow food within 60 years. [3] Clearly this is a major issue that needs to be addressed.
Topsoil is more than just dirt, it is a living thing made up of countless microorganisms [3-5] The Earth is covered with an average of three feet of topsoil, the layer of dirt that provides the nutrients for most of the planet's land vegetation, and is critical for producing food from agriculture. [5] Good topsoil maximizes crop yield while protecting the crop from degradation. The quantity of soil eroded is determined by multiple factors; including weather (wind and rain), the surface the soil (including the steepness on slope the soil is on), and the cover on the soil surface (i.e. plants or trees). [4] Soil erodes and then replenishes naturally at a rate of only an inch or two per several hundred years. [5] A problem only arises when soil erodes at an accelerated rate and cannot be replenished quickly enough. Accelerated erosion occurs when the energy from rain or wind contacts bare soil, detaching bits from the surface. [4]
Industrial farming practices such as tilling and use of agrochemicals, as well as deforestation to produce farmland have dramatically increased the rate of soil erosion. Around the world, topsoil is vanishing much faster than it forms According to David Montgomery, a geologist at the University of Washington, its clear that we're losing more and more topsoil every day. "The estimate is that we are now losing about 1 percent of our topsoil every year to erosion, most of this caused by agriculture." [5] The United States is losing soil at a rate 10 times faster than the soil replenishment rate while China and India are losing soil 30 to 40 times faster. [6] With soil erosion rates so much higher than the replenishment rate, it is no wonder that the world is quickly running out of fertile topsoil. Table 1 shows the severity of topsoil degradation worldwide.
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| Table 1: Estimates of all degraded lands (in million km2) in dry areas. [11] |
The most visible effect of topsoil topsoil erosion is the decreasing crop yields. Soil erosion makes it more difficult for the soil to store water and support plant growth. Erosion can cause yield reductions of 30 to 90% in some root-restrictive shallow lands of West Africa. [7] Nationally, It is estimated that the total annual cost of erosion from agriculture in the USA is about US$44 billion per year. [8] Given that freshwater is becoming a scarce and valuable resource in our world, it is will become increasingly important that we use as little water as possible to grow crops. [9]
Soil erosion also contributes to environmental damage (see Fig. 1). In addition to promoting water loss, it results in loss of nutrients, soil organic matter and soil biota, harming forests, rangeland and natural ecosystems. [2] Erosion increases the amount of dust carried by wind, which not only acts as an abrasive and air pollutant but also carries about 20 human infectious disease organisms, including anthrax and tuberculosis. [2] Finally, about 60 percent of soil that is washed away ends up in rivers, streams and lakes, making waterways more prone to flooding and to contamination from soil's fertilizers and pesticides. [2]
Technological farming advances have helped mask some of the effects of soil erosion, but may have served to deflect attention from the problem rather than helping to solve the problem. However, there are many ways that we can help mitigate the problem of soil erosion. Farmers switching to no-till farming would help greatly reduce topsoil erosion (although there are downsides to switching to no-till for farmers such as requires heavy upfront investment and learning new techniques and also tends to depend more on herbicides because the weeds are no longer controllable by plowing them into the soil, so farmers may need to be compensated to encourage these changes. [5] Leaving stubble after harvest rather than burning it off or rotating crops to add vegetative cover will also slow some soil loss. [3] Finally, in areas with slopes, adding terraces would provide increased protection from runoff damage by reducing slope lengths and the energy of water available to carry soil off of fields. These changes take effort and money, and in order for them to be made, farmers need to be incentivized so that topsoil preservation is taken into account.
Topsoil erosion may not currently be a mainstream issue, but it is undoubtedly a huge problem that will continue to increase in stature if changes are not implemented. With arable land in the world shrinking and the population growing, scientists are already looking into alternate locations such as the moon or possibly Mars to grow food. A recent study has shown these locations to hypothetically be viable. [10] However, while the results of this study are exciting, we still have a long way to go to making it a reality and it would be advisable to mitigate topsoil erosion on our planet.
© Eric Verso. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] Attitudes About Aging: A Global Perspective," Pew Research Center, January 2014.
[2] D. Pimentel, "Soil Erosion: A Food and Environmental Threat," Environ. Devel. Sustain. 8, 119 (2006).
[3] "What If the World's Soil Runs Out?" Time, 14 Dec 12.
[4] D. R. Montgomery, "Soil Erosion and Agricultural Sustainability," Proc. Nat. Acad. Sci. (USA) 104, 133268 (2007).
[5] D. R. Montgomery, Dirt: The Erosion of Civilizations, 2nd Ed. (University of California Press, 2012).
[6] S. Lang, "'Slow, Insidious' Soil Erosion Threatens Human Health and Welfare as Well as the Environment, Cornell Study Asserts," Cornell Chronicle, 20 Mar 06.
[7] R. Lal, "Erosion-Crop Productivity Relationships for Soils of Africa," Soil Sci. Soc. Am. J. 59, 661 (1995).
[8] H. Eswaran, R. Lal, and P. F. Reich, "Land Degredation: An Overview," in Response to Land Degradation, ed. by E. M. Bridges et al. (Science Pub. Inc., 2001).
[9] R. Clark, Water The International Crisis (Earthscan, 1991).
[10] G. W. Wamelink et al., "Can Plants Grow on Mars and the Moon: A Growth Experiment on Mars and Moon Soil Simulants," PLoS ONE 9, e103138 (2014).
[11] H. E. Dregne, "Land Degradation in the Drylands," Arid Land Res. Manage. 16, 99 (2002).
